The objectives of this study are 1) to relate current classification schemes for motor units of hindlimb skeletal muscle to those of the forelimb and specialized muscles such as the masseter and temporalis in the mammals: guinea pig, cat and Lesser Bushbaby; and 2) to gather information regarding how these mechanically and metabolically distinct types of muscle fibers are used in simplified isometric and isotonic contractions and in more complex movement such as walking, running, jumping and weight lifting. This information is being obtained by chronically implanting multistranded stainless steel wire into muscles that are predominantly slow- or fast-twitch and recording raw and integrated electromyography while the animal is performing specific movements. The movements are monitored and matched to the EMG with a video special effects generator. Muscle glycogen is being related to changes in EMG after running on a treadmill and after repetitive nerve stimulation of an in situ gastrocnemius-soleus muscle preparation. BIBLIOGRAPHIC REFERENCES: Edgerton, V.R., Barnard, R.J., Peter, .B., Maier, A., and Simpson, D.R. Properties of immobilized hindlimb muscles of the Galago senegalensis. Exp. Neurol. 46: 115-131, 1975. Botterman, B. R., and Edgerton V.R., Histochemical profiles of rat soleus intrafusal fibers after chronic exercise. Histochem. J. 7: 151-164, 1975.